Holographic sensors and their production

Abstract

A method for the production of a holographic sensor wherein the holographic recording material forming the sensitive element is a polymer matrix, which comprises diffusing into the matrix one or more soluble salts that undergo reaction in situ to form an insoluble sensitive precipitate; and recording a holographic image. This method allows the production of a holographic sensor wherein the holographic recording material forming the sensitive element is an insoluble polymer film.

Description

This invention relates to a chemical sensor based on a sensitive element which is a hologram made from a silver halide-based recording material.BACKGROUND TO THE INVENTIONMany different approaches to producing chemical sensors have been described in the academic and patent literature. There exists a wide range of different transduction mechanisms, which can be married with a suitable chemical or biochemical interface to realise a more or less selective sensor capable of identifying and / or quantitating a particular chemical substance. Transducers that have been successfully applied include those harnessing electrical, acoustic or optical phenomena.WO-A-9526499 discloses a new class of optical sensor, the holographic chemical sensor, based on a volume hologram. This configuration has the unique feature that the analyte-sensitive matrix film has the optical transducing structure disposed throughout its volume. Because of this physical arrangement of the transducer, the optical signal g...

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Problems solved by technology

To date, however, few suitable holographic film materials exist.

The materials from which they are made and their structures render them unsuitable for sensing applications.

Applications of gelatin to chemical sensing are severely restricted by its complex chemical nature and hence the difficulty of chemically derivatising it in a rational way in order to change its analyte selectivity.

PVA-based holograms have some advantages over gelatin, but they are still very restricted in their scope, due to the incompatibility between the sensitive silver halide colloidal particles and the conditions required to chemically transform the PVA into a stable and analyte-selective matrix.

Other types of holographic recording material known to those skilled in the art are also unsuitable for a variety of reasons.

For example, when holograms made by the dichromating method are immersed in liquid, the voids fill up and the refractive index modulation is lost; hence these materials are entirely unsuitable for use as liquid phase chemical or biochemical sensors.

Photopolymer holograms are either uncross-linked or are only cross-linked in the areas of light exposure during hologram recording, and thus are not stable to immersion in solvents of the polymers from which they are made.

Such solvent exposure disrupts the ordered layer structure of the hologram.

Many photopolymer formulations are also very hydrophobic and hence incompatible with aqueous solutions of analytes, which are incapable of penetrating the hologram.

Due to the problems with other types of holographic recording material, and also because of ease of handling and unrivalled sensitivity to light, silver halide-based films remain the materials of choice for realising holographic chemical sensor devices.

However, the liquid phase colloid method is inapplicable to the types of custom-designed polymer materials which are required for analyte-selective chemical sensing.

This is because the chemical conditions required to make suitable custom-designed polymer films are not compatible with the silver halide colloid formation process, and often lead to insoluble cross-linked materials.

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